Optical pickup device and optical disc apparatus

ABSTRACT

An optical pickup device including: a laser diode for emitting laser light; an objective lens which irradiates an optical beam emitted from the laser diode; an actuator which displaces the objective lens in a radius direction of the optical disc; a grating for branches an optical beam reflected by an information recording layer into plural regions; and one photodetector having plural light receiving parts for receiving the branched optical beams, wherein the photodetector has a first light receiving part which detects zero-th order grating diffracted light and plural second light receiving parts which detecting grating diffracted light having an order not less than that of ±first order grating diffracted light; a detected signal of the zero-th order grating diffracted light is defined as a reproduction signal; and a detected signal of the grating diffracted light is defined as a signal for servo controlling.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese applicationJP-2010-041267 filed on Feb. 26, 2010, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to an optical pickup device and an opticaldisc apparatus.

As a background art of this technical field, for example, there isJP-A-2006-344344 which describes an object “to precisely obtain desiredsignals from an optical disk having a plurality of recording layers”,and discloses a solution as follows: “an optical beam of P-polarizedlight emitted from a light source unit 51 is reflected by an opticaldisc 15 and becomes S-polarized light to enter a lens 61. Then, both ofquarter wave plates 62 and 63 impart an optical phase difference of a+quarter wavelength to the optical beam having entered an +X side of anoptical axis, and impart an optical phase difference of a −quarterwavelength to the optical beam having entered the −X side. Thus, signallight through the quarter wave plate 63 becomes S-polarized light, andstray light becomes P-polarized light, so that a polarization opticalelement 64 transmits only the signal light.”

Further, in JP-A-2009-170060, there is described “it is an object toprovide an optical pickup device capable of providing stable servosignals by preventing the influence of stray light from other layers ona focusing error signal and tracking error signal during recording andreproducing operations in a multilayer optical disc.” A solution isdisclosed as follows: “reflected light from the multilayer optical discis divided into a plurality of regions, divided luminous fluxes arefocused on different positions of a photodetector, the focusing errorsignal is detected by a knife edge method using a plurality of thedivided luminous fluxes, and the tracking error signal is detected byusing the plurality of divided luminous fluxes”. Further, “when a focusis on an intended layer, the divided region of a luminous flux and alight receiving surface are arranged so as to prevent incidence of straylight from the other layers to a light receiving surface for the servosignal of the photodetector.”

SUMMARY OF THE INVENTION

An optical pickup device correctly irradiates an optical spot on apredetermined recording track which is generally present within anoptical disc and therefore, detects a focusing error signal anddisplaces an objective lens in a focus direction to perform anadjustment in the focus direction. In addition, the optical pickupdevice detects a tracking error signal and displaces the objective lensin a radius direction of the optical disc to perform a trackingadjustment. The optical pickup device performs a position control of theobjective lens using these servo signals.

There is a significant problem as to the tracking error signal among theabove-described servo signals that a multilayer disc in which aplurality of recording layers are present are used. In the multilayerdisc, in addition to signal light reflected by the intended recordinglayer, stray light reflected by a plurality of unintended recordinglayers enters the same light receiving part. When the signal light andthe stray light enter the light receiving part, both of optical beamsinterfere, and as a result, its fluctuating component is detected in thetracking error signal.

To cope with the above-described problem, the optical pickup devicedisclosed in JP-A-2006-344344 has a construction in which an opticalbeam reflected by the optical disc is focused by a condenser lens; thefocused optical beam passes through two sheets of the quarter waveplates and a polarization optical element and further, a widened opticalbeam is focused by the condenser lens, and as a result, stray light isprevented from entering a photodetector. Therefore, there is a problemthat the construction of the optical detecting system becomes complex,and a size of the optical pickup device becomes large.

Further, the optical pickup device disclosed in JP-A-2009-170060 has aconstruction in which, since a reproduced signal is detected using aplurality of light receiving parts on the photodetector, noisesgenerated at the time of converting light into electric signals areadded to the reproduced signal. Therefore, there is a problem ofreducing the noise of the reproduced signal, that is, improving asignal-to-noise ratio.

It is an object to provide an optical pickup device capable of reducingthe noise of the reproduced signal, acquiring stable servo signals, andminiaturizing than ever before in such a case that an informationrecording medium having a plurality of information recording layers isrecorded or reproduced, and also to provide optical disc apparatus onwhich the above-described optical pickup device is mounted.

The above-described object can be achieved by the present inventiondisclosed in the scope of claims.

According to an aspect of the present invention, there is provided anoptical pickup device capable of reducing the noise of the reproducedsignal, acquiring stable servo signals, and miniaturizing than everbefore in such case that the information recording medium having theplurality of information recording layers is recorded or reproduced, andalso there is provided optical disc apparatus on which theabove-described optical pickup device is mounted.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an optical system according to a first embodiment ofthe present invention.

FIG. 2 illustrates a grating according to the first embodiment of thepresent invention.

FIG. 3 illustrates light receiving parts according to the firstembodiment of the present invention.

FIG. 4 illustrates a shape (on a photodetector) of stray light at thetime when recorded on or reproduced from a dual layer disc in the firstembodiment of the present invention.

FIG. 5 illustrates a behavior of the stray light from other layers ofthe dual layer disc.

FIG. 6 illustrates a behavior of the stray light from other layers ofthe dual layer disc.

FIGS. 7A and 7B illustrate other gratings in the first embodiment of thepresent invention.

FIG. 8 illustrates another grating in the first embodiment of thepresent invention.

FIG. 9 illustrates other light receiving parts in a different array inthe first embodiment of the present invention.

FIG. 10 illustrates other light receiving parts in a different array inthe first embodiment of the present invention.

FIG. 11 illustrates other light receiving parts according to a secondembodiment of the present invention.

FIG. 12 illustrates other light receiving parts in a different array inthe second embodiment of the present invention.

FIGS. 13A and 13B illustrate other light receiving parts in a differentarray, respectively, in the second embodiment of the present invention.

FIGS. 14A and 14B illustrate other light receiving parts in a differentarray, respectively, in the second embodiment of the present invention.

FIGS. 15A and 15B illustrate other light receiving parts in a differentarray, respectively, in the second embodiment of the present invention.

FIG. 16 illustrates light receiving parts according to a thirdembodiment of the present invention.

FIG. 17 illustrates a shape (on a photodetector) of stray light at thetime when recorded on or reproduced from a dual layer disc in the thirdembodiment of the present invention.

FIGS. 18A and 18B illustrate other light receiving parts in a differentarray, respectively, in the third embodiment of the present invention.

FIG. 19 illustrates other light receiving parts in a different array inthe third embodiment of the present invention.

FIG. 20 illustrates light receiving parts according to a fourthembodiment of the present invention.

FIGS. 21A and 21B illustrate other light receiving parts in a differentarray, respectively, in the fourth embodiment of the present invention.

FIGS. 22A to 22C illustrate other light receiving parts in a differentarray, respectively, in the fourth embodiment of the present invention.

FIGS. 23A to 23D illustrate other light receiving parts in a differentarray, respectively, in the fourth embodiment of the present invention.

FIGS. 24A to 24D illustrate other light receiving parts in a differentarray, respectively, in the fourth embodiment of the present invention.

FIG. 25 illustrates an optical reproducing device according to a fifthembodiment of the present invention.

FIG. 26 illustrates an optical recording and reproducing deviceaccording to a sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings of theembodiments.

First Embodiment

FIG. 1 illustrates an optical system of an optical pickup deviceaccording to a first embodiment of the present invention. Here, althougha BD (Blu-ray Disc) will be described, a DVD (Digital Versatile Disc) orother recording systems may be optionally applicable. Note that layersof an optical disc include a recording layer of a recording optical discand a reproducing layer of a reproduction-only optical disc in thefollowing description.

An optical beam having a wavelength of approximately 405 nm is emittedfrom a laser diode 50 as divergent light. The optical beam emitted fromthe laser diode 50 is reflected by a beam splitter 52. Note that aportion of the optical beam passes through the beam splitter 52 and thenenters a front monitor 53. Generally, in such a case that information isrecorded on the recording type optical disc, the light amount of thelaser diode is required to be controlled with a high degree of accuracyin order that a predetermined light amount of the laser diode may beirradiated onto the information recording surface (recording layer) ofthe recording type optical disc. To this end, when a signal is recordedon the recording type optical disc, the front monitor 53 detects achange in the light amount of the laser diode 50 and feeds back thedetected light change amount to a driving circuit (not illustrated) ofthe laser diode 50. As a result, the front monitor 53 can monitor thelight amount on the optical disc.

The optical beam reflected by the beam splitter 52 is converted into asubstantially parallel optical beam by a collimating lens 51. Theoptical beam that passed through the collimating lens 51 enters a beamexpander 54. The beam expander 54 is utilized in order to compensatespherical aberration due to a thickness error of a cover layer of theoptical disc, by changing the divergent/convergent state of an opticalbeam. The optical beam emitted from the beam expander 54 is reflected bya reflection mirror 55 and passes through a quarter wave plate 56. Then,the optical beam is focused on the optical disc by an objective lens 2mounted on an actuator 5.

The optical beam reflected by the optical disc passes through theobjective lens 2, the quarter wave plate 56, the reflection mirror 55,the beam expander 54, the collimating lens 51, and the beam splitter 52,and then enters a grating 11. The entered optical beam is divided into aplurality of regions by the grating 11 and the divided optical beamstravel along directions that are different from each other with respectto these plural regions and are focused on a photodetector 10. While aplurality of light receiving parts have been formed on the photodetector10, the plurality of optical beams divided by the grating 11 areirradiated onto the respective light receiving parts. Electric signalsare output from the photodetector 10 in response to the light amount ofthe optical beams irradiated on the light receiving parts, and theseoutput electric signals are calculated so as to generate an RF signal, afocusing error signal, and a tracking error signal as reproductionsignals.

Detection of the tracking error signal will be described here. As ageneral method for detecting the tracking error signal, a 3-beamdifferential push pull method (DPP: Differential Push Pull method) forirradiating three optical beams on an optical disc is known. Accordingto this 3-beam DPP method, an optical beam is divided by the grating 11into a main beam, a sub beam +first order diffracted light, and a subbeam −first order diffracted light, and forms three spots on the opticaldisc. At this time, disc reflected light from three spots is detected,and a main push pull (MPP) signal obtained from a main beam and sub pushpull (SPP) signals obtained from the sub beam +first order diffractedlight and the sub beam −first order diffracted light are calculated asfollows to detect a 3-beam DPP signal subtracted with a DC componentaccompanied by the displacement of an objective lens.

DPP=MPP−k×SPP  [Equation 1]

Note that a symbol “k” is a coefficient for correcting a light amountratio between the main beam and the sub beams.

However, as to the 3-beam DPP system, a problem occurs at the time ofrecording and reproducing operations of an optical disc having recordinglayers of two layers or more. The above-described problem will bedescribed using a simplest dual layer disc. The dual layer disc is anoptical disc with two recording layers, and an optical beam is reflectedby each recording layer. Therefore, in the dual layer disc, an opticalbeam is separated into two parts by the optical disc and each separatedpart enters the photodetector through two optical paths. For example,when focusing one layer, the optical beam forms a spot (signal light) ona surface of the photodetector and an optical beam (stray light)reflected by the other layer enters the photodetector in an indistinctstate. At this time, the signal light and the stray light reflected byrespective layers overlap each other on the photodetector, andinterference occurs. Fundamentally, optical beams emitted from a laserdiode with the same frequency do not change in time. However, since adistance between the layers changes due to a rotation of the opticaldisc, a phase relationship between two optical beams changes with time,and variation of the DPP signal serving as the tracking error signal iscaused. This variation of the 3-beam DPP signal is mainly caused by theSPP signal. The reason is as follows. The light amount ratio of the mainbeam (zero-th order diffracted light), the sub beam +first orderdiffracted light, and the sub beam −first order diffracted light isgenerally from 10:1:1 to 20:1:1, and the light amount of the sub beam issmall as compared with that of the main beam. Therefore, interferencebetween the signal light of the sub beam and the stray light of the mainbeam largely occurs with respect to the signal light. This permits theSPP signal to largely change, and as a result, the 3-beam DPP signal asthe tracking error signal largely changes. When the variation of thetracking error signal occurs, a spot on the optical disc fails to followalong a track, and there mainly occurs the problem of performancedegradation of the recording and reproducing operations.

To cope with the above-described problem, in JP-A-2006-344344, anoptical pickup device has a construction in which an optical beamreflected by the optical disc is focused by a condenser lens and anoptical beam spread by passing through two sheets of quarter waveplates, and a polarization optical element is focused by a condenserlens, so that the stray light is prevented from entering thephotodetector. Therefore, there is a problem that the detection opticalsystem becomes complicated and the size of the optical pickup deviceincreases.

As compared with the above-described optical pickup device, the opticalpickup device according to the present embodiment has an extremelysimple optical system as illustrated in FIG. 1, and therefore, can beminiaturized. Hereinafter, the optical pickup device according to thepresent embodiment will be described.

FIG. 2 illustrates a shape of the grating 11 according to the presentembodiment. A solid line illustrates a boundary line of regions, a chaindouble-dashed line illustrates an outer shape of an optical beam, and ahatched portion illustrates an interference region (push-pull pattern)between zero-th order disc diffracted light and ±first order discdiffracted light of diffracted light (hereinafter, referred to as “discdiffracted light”) diffracted by the tracks of the optical disc. Thegrating 11 is formed by regions “De”, “Df', “Dg”, and “Dh” (region “A”)to which only the zero-th order disc diffracted light of the discdiffracted light diffracted by the tracks on the optical disc enters;regions “Da”, “Db”, “Dc”, and “Dd” (region “B”) to which the zero-thorder disc diffracted light and the ±first order disc diffracted lightof the disc diffracted light enters; and also, a region “Di” (region“C”). The photodetector 10 has a pattern as illustrated in FIG. 3. Notethat black points indicate the zero-th order grating diffracted lightand ±first order grating diffracted light of the diffracted light(hereinafter, referred to as “grating diffracted light”) diffracted bythe grating 11 in the drawing. Suppose that a spectral ratio of thegrating 11 is, for example, the zero-th order grating diffracted light:the +first order grating diffracted light: the −first order gratingdiffracted light=10:1:1.

In this case, the zero-th order grating diffracted light diffracted bythe regions Da, Db, Dc, Dd, De, Df, Dg, Dh, and Di of the grating 11enters a light receiving part j of the photodetector illustrated in FIG.3. Further, the +first order grating diffracted light diffracted by theregions Da, Db, Dc, Dd, De, Df, Dg, and Dh of the grating 11 enters thelight receiving parts a1, b1, c1, d1, e1, f1, g1, and h1, respectively.Further, the −first order grating diffracted light diffracted by theregions Da, Db, Dc, and Dd enters the light receiving parts r, s, t, u,v, w, x and y for detecting a focusing error signal, respectively,whereas the −first order grating diffracted light diffracted by theregions De, Df, Dg, and Dh enters the light receiving parts e2, f2, g2,and h2, respectively. Signals J0, A1, B1, C1, D1, E1, F1, G1, H1, E2,F2, G2, H2, R, S, T, U, V, W, X, and Y obtained from the light receivingparts j, a1, b1, c1, d1, e1, f1, g1, h1, e2, f2, g2, h2, r, s, t, u, v,w, x, and y, are processed based upon the below-mentioned calculationsin order to generate a focusing error signal (FES), a tracking errorsignal (TES), and an RF signal (RF).

$\begin{matrix}{\mspace{79mu} {{{FES} = {\left( {S + T + W + X} \right) - \left( {R + U + V + Y} \right)}}{{TES} = {\quad{{\left\lbrack {\left\{ {\left( {{A\; 1} + {E\; 1}} \right) + \left( {{B\; 1} + {F\; 1}} \right)} \right\} - \left\{ {\left( {{C\; 1} + {G\; 1}} \right) + \left( {{D\; 1} + {H\; 1}} \right)} \right\}} \right\rbrack - {{kt} \times \left\{ {\left( {{E\; 2} + {F\; 2}} \right) - \left( {{G\; 2} + {H\; 2}} \right)} \right\} \mspace{79mu} {RF}}} = {J\; 0}}\mspace{40mu}}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Note that a symbol kt is a coefficient so as not to generate a DCcomponent in the tracking error signal when the objective lens isdisplaced. In this case, for example, the knife edge method is used asthe focus error detection method.

Since an RF signal is generated from the signal J0 obtained from onelight receiving part j on the photodetector, the above-described methodexerts an effect of reducing noises generated at the time of convertinglight into the electric signal as compared with the method in which anRF signal is generated from a signal obtained from a plurality of lightreceiving parts on the photodetector as disclosed in, for example,JP-A-2009-170060. Hereinafter, an embodiment for avoiding multilayerstray light in this method will be described in detail.

FIG. 4 illustrates a relationship between signal light and stray lightfrom other layers during recording and reproducing operations of thedual layer disc. FIG. 4 (a) illustrates a relationship between thesignal light and the stray light from the other layers during recordingand reproducing operations of an L0 layer, and FIG. 4 (b) illustrates arelationship between the signal light and the stray light from otherlayers during recording and reproducing operations of an L1 layer. Here,one stray light O0 and another stray light O1 indicate the zero-th ordergrating diffracted light of stray light from the other layers of the L0layer and the L1 layer, respectively. As can be seen from FIG. 4, thesignal light and the stray light from the other layers do not overlapeach other on the light receiving part except for the zero-th ordergrating diffracted light of the grating 11. The signal J0 detected fromthe light receiving part j is not used for detecting the tracking errorsignal, but used for a reproduction signal. Therefore, even if the straylight is present, there is no problem from a practical standpoint.

From FIG. 4, since the stray light from the other layers is preventedfrom entering the light receiving part for detecting the tracking errorsignal, interference between the signal light and the stray light doesnot occur. Therefore, the optical pickup device can detect stabletracking error signals. Further, the optical pickup device according tothe present embodiment has a construction in which even if the objectivelens is displaced, the stray light is hard to enter the light receivingpart.

When the signals are actually detected, the object lens records orreproduces the signals along with following the tracks formed on anoptical disc, so that the objective lens is displaced in a Raddirection. Therefore, in the case of using the normal pattern of thelight receiving part of the photodetector, there is a possibility thatwhen the objective lens is displaced, the stray light from the otherlayers enters the light receiving part. In contrast to theabove-explained general situation, the optical pickup device accordingto the present embodiment, the light receiving parts of thephotodetector 10 are optimized with respect to the patterns of thegrating 11, so that an allowable amount of the displacement of theobjective lens can be increased. In this case, the matter which shouldbe considered is how the signal light is separated from the stray lightwith respect to the displacement direction of the objective lens.

FIG. 5 illustrates an optical beam which has been diffracted by theregion Dh of the grating 11 and then has entered the light receivingpart h1, and FIG. 6 illustrates an optical beam which has beendiffracted by the region Dd of the grating 11 and then has entered thelight receiving part d1. (a), (b), and (c) have been divided dependingupon states of optical spots on an optical disc. (b) illustrates a stateunder which the optical beams are focused on the optical discs, whereas(a) and (c) illustrate states under which the optical beams aredefocused by the objective lens. In addition, in (a) and (c), thedirection in which the optical beams are defocused by the objective lensis different from each other. Note that a relationship among the symbols(a) to (c) does not substantially depend upon the positions of the lightreceiving parts. The reason why the defocused states are described isthat it can be interpreted that the stray light emitted from the duallayer disc corresponds to the defocused light reflected by such aposition which is not a focal position.

When the optical beam states illustrated in FIG. 5 are compared withthose illustrated in FIG. 6, it can be understood that optical beammoving directions are different from each other due to defocusing. Theoptical beam diffracted by the region Dh of FIG. 5 moves along a trackdirection (will be referred to as Tan direction hereinafter) of theoptical disc by being defocused. In contrast thereto, the optical beamdiffracted by the region Dd of FIG. 6 moves along the radial direction(Rad direction). The reason is that since the optical beams are blurredin a point symmetrical manner with respect to a center 15 of the opticalbeams on the grating 11, the optical beam moving directions due to thedefocusing depending on the regions are different from each other. As aresult, it becomes important that how to avoid the stray light areclassified depending upon the regions. In such a case that regions ofthe grating 11 have been separated along the Tan direction with respectto the optical beam center 15 (namely, regions Dh, De, Df, Dg (regionA)), it is desirable to avoid the stray light along the Tan direction.By avoiding the stray light in the above-described manner, even when theobjective lens displaces along the Rad direction, this stray light isprevented from entering the photodetector. As a consequence, the lightreceiving parts for detecting the optical beams diffracted by theregions Dh, De, Df, Dg of the grating 11 are arranged along the Raddirection, so that adverse influences caused by the stray lightdiffracted by the other regions can be suppressed to a minimum effect.

Also, in such a case that regions of the grating 11 have been separatedalong the Rad direction with respect to the optical beam center 15(namely, regions Da, Db, Dc, and Dd (region B)), it is desirable toavoid the stray light along the Rad direction. As a consequence, thelight receiving parts for detecting the optical beams diffracted by theregions Da, Db, Dc, Dd of the grating 11 are arrayed along the Tandirection, so that adverse influences caused by the stray lightdiffracted by the other regions can be suppressed to a minimum effect.

As described above, when the light receiving parts are arranged asillustrated in FIG. 3, the signal light and the stray light can beeffectively separated from each other. Therefore, the photodetector 10can detect the stable tracking error signal.

Further, by performing the detection of the RF signals by one lightreceiving part as described above, noises generated at the time ofconverting light into electric signals can be reduced, so that thisconstruction is extremely advantageous from the viewpoint of theimprovement in the signal-to-noise ratio of reproduction signals in themultilayer disc.

According to the present embodiment, the grating 11 is described withreference to FIG. 2, however, it is not limited thereto. For example,even if the patterns as illustrated in FIGS. 7A and 7B are used, asimilar effect can be obtained. Further, for the purpose of eliminatingthe stray light except within an effective diameter of the signal lighton the grating 11, if a region Z is formed on the grating 11 asillustrated in FIG. 8, a similar effect can be obtained. In this case,the grating 11 has a construction such that light entering the region Zis prevented from entering the light receiving parts. The region Z maybe made by a grating structure, a multilayer-film mirror, or a filter.Moreover, in the first embodiment, the grating 11 was arranged at theposition after the optical beam has passed through the beam splitter 52.Alternatively, along with replacing the grating 11 by a polarizingdiffracted grating, if the polarizing diffracted grating may be arrayedat a position before the optical beam passes through the beam splitter52, a similar effect can be obtained. Also, although the optical dischaving two layers has been described in the first embodiment, even whensuch optical discs having three or more layers are used, a similareffect can be obtained. In addition, as apparent from the foregoingdescription, there is no limitation as to the spherical aberrationcompensation method. The arrangement of the light receiving partsaccording to the present embodiment is one example. If the zero-th ordergrating diffracted light of the grating 11 with a large light amount isdetected using one light receiving part and the light receiving partsfor the ±first order grating diffracted light diffracted by the grating11 or those for the grating diffracted light with the order larger thanthe first order are arranged so as to avoid the stray light of thezero-th order grating diffracted light, a similar effect can beobtained. Further, if the stray light of the regions in the Raddirection with respect to the grating center is separated from eachother in the Rad direction, while if the stray light of the regions inthe Tan direction with respect to the grating center is separated fromeach other in the Tan direction, it goes without saying that a similareffect can be obtained. For example, even if the light receiving partse1, f1, g1, and h1 (the light receiving parts e2, f2, g2, and h2) arearrayed in the Rad direction as illustrated in FIG. 9 for the opticalbeams diffracted by the regions Dh, De, Df, and Dg (region A) theregions of which on the grating 11 is separated from each other in theTan direction, it goes without saying that a similar effect can beobtained. In addition, the light receiving parts a1, b1, c1, d1, e1, f1,g1, and h1, the light receiving part for detecting the focus signal, andthe light receiving parts e2, f2, g2, and h2 may be arrayed so as toform an approximately circular shape with respect to the zero-th ordergrating diffracted light as illustrated in a dotted line 24 of FIG. 9.

The optical pickup device according to the present embodiment ischaracterized by a construction in which the stray light is preventedfrom entering the light receiving parts, and does not depend upon themethods for detection and the calculations of the focusing error signaland the tracking error signal. Therefore, even if the +first ordergrating diffracted light is replaced by the −first order gratingdiffracted light in the light receiving part for detecting the focusingerror signal, for example, as illustrated in FIG. 10, a similar effectmay be obtained. Further, there is no need for both of the lightreceiving parts to be contacted with each other. Although, in thepresent embodiment, the +first order grating diffracted light and the−first order grating diffracted light of the region Di were notspecified, for example, the +first order grating diffracted light andthe −first order grating diffracted light may be diffracted in the Raddirection, and signals for adjustment and other servo signals such as aspherical aberration error signal may be detected by using them.Furthermore, output signals from the optical pickup device may bereduced by connecting the light receiving parts by wires.

Second Embodiment

FIG. 11 illustrates light receiving parts of a photodetector of anoptical pickup device according to a second embodiment of the presentinvention. A structural difference from the first embodiment is thephotodetector 10 and the other structural elements of the secondembodiment are similar to those of the first embodiment.

The grating 11 illustrated in FIG. 2 is formed by the regions De, Df,Dg, and Dh (region A) entered by only the zero-th order disc diffractedlight of the disc diffracted light diffracted by the tracks on theoptical disc, the regions Da, Db, Dc, and Dd (region B) entered by thezero-th order disc diffracted light and the ±first order disc diffractedlight of the disc diffracted light, and the region Di (region C).

Suppose that a spectral ratio of the grating 11 is, for example, thezero-th order grating diffracted light: the +first order gratingdiffracted light: the −first order grating diffracted light=10:1:1. Thephotodetector 10 has a pattern as illustrated in FIG. 11. In thedrawing, black points illustrate the zero-th order grating diffractedlight and the ±first order grating diffracted light diffracted by thegrating. In this case, the zero-th order grating diffracted lightdiffracted by the regions Da, Db, Dc, Dd, De, Df, Dg, Dh, and Di of thegrating 11 enters the light receiving part j of the photodetectorillustrated in FIG. 11. Further, the +first order grating diffractedlight diffracted by the regions Da, Db, Dc, Dd, De, Df, Dg, and Dh ofthe grating 11 enters the light receiving parts a1, b1, c1, d1, e1, f1,g1, and h1, respectively. Further, the −first order grating diffractedlight diffracted by the regions Da, Db, Dc, and Dd enters the lightreceiving parts r, s, t, u, v, w, x, and y for detecting a focusingerror signal, respectively. Here, the −first order grating diffractedlight diffracted by the regions De, Df, Dg, and Dh is prevented fromentering the light receiving parts, respectively.

Signals J0, A1, B1, C1, D1, E1, F1, G1, H1, R, S, T, U, V, W, X, and Yobtained from the light receiving parts j, a1, b1, c1, d1, e1, f1, g1,h1, r, s, t, u, v, w, x, and y are calculated as follows to generate thefocusing error signal (FES), the tracking error signal (TES), and the RFsignal (RF).

FES=(S+T+W+X)−(R+U+V+Y)

TES=[(A1+B1)−(C1+D1)]−kt×[(E1+F1)+(G1+H1)]

RF=J0  [Equation 3]

Note that a symbol kt is a coefficient used so as not to generate a DCcomponent in the tracking error signal when the objective lens isdisplaced. In this case, for example, the knife edge method is used asthe focus error detection method. Since optical spots are arranged onthe photodetector in the same manner as in the first embodiment, thestray light from the other layers during the recording and reproducingoperations of the dual layer disc is prevented from entering the lightreceiving parts except for the zero-th order grating diffracted light ofthe grating 11. Note, however, that the signal J0 detected from thelight receiving part j is not used for detecting the tracking errorsignal, but used for a reproduction signal. Therefore, even if the straylight is present, there is no problem from a practical standpoint.

Also as described in the first embodiment, in such a case that regionsof the grating 11 are separated along the Tan direction with respect tothe optical beam center 15 (namely, regions Dh, De, Df, and Dg (regionA), it is desirable that the stray light is avoided along the Tandirection. Therefore, by avoiding the stray light along the Tandirection as in the light receiving parts e1, f1, g1, and h1 in FIG. 11,the stray light is prevented from entering the light receiving parts,even if the objective lens is displaced in the Rad direction.

In such a case that regions of the grating 11 have been separated alongthe Rad direction with respect to the optical beam center 15 (namely,regions Da, Db, Dc, Dd (region B), it is desirable to avoid the straylight along the Rad direction. Therefore, by avoiding the stray lightalong the Rad direction as in the light receiving parts a1 and b1, andc1 and d1 in FIG. 11, adverse influences caused by the stray lightdiffracted by the other regions can be suppressed to a minimum effect.

As described above, when the light receiving parts are arranged asillustrated in FIG. 11, the photodetector 10 can effectively separatethe signal light from the stray light. Therefore, the photodetector 10can detect stable tracking error signals. Further, when the detection ofRF signals is performed by one light receiving part as described above,noises generated at the time of converting light into electric signalscan be reduced, so that the above-described construction is extremelyadvantageous from the viewpoint of the improvement in thesignal-to-noise ratio of reproduction signals in the multilayer disc.

According to the present embodiment, the grating 11 is described withreference to FIG. 2, however, it is not limited thereto. For example,even if the grating 11 has a pattern as illustrated in FIGS. 7A and 7B,a similar effect can be obtained. Further, for the purpose ofeliminating the stray light except within an effective diameter of thesignal light on the grating 11, if a region Z is formed on the grating11 as illustrated in FIG. 8, a similar effect can be obtained. At thistime, the grating 11 has a construction in which light that enters theregion Z is prevented from entering the light receiving parts. Theregion Z may be made by a grating structure, a multilayer-film mirror,or a filter. Moreover, in the present embodiment, the grating 11 hasbeen arranged at the position after the optical beam has passed throughthe beam splitter 52. Alternatively, along with replacing the grating 11by a polarization diffracted grating, if the polarization diffractedgrating may be arrayed at a position before the optical beam passesthrough the beam splitter 52, it goes without saying that a similareffect can be obtained. Also, although the optical disc having twolayers has been described in the present embodiment, even when suchoptical discs having three or more layers may be used, a similar effectcan be obtained. In addition, as apparent from the foregoingdescription, there is no limitation as to the spherical aberrationcompensation method. The arrangement of the light receiving partsaccording to the present embodiment is one example. If the zero-th ordergrating diffracted light of the grating with a large light amount isdetected using one light receiving part and the light receiving partsfor the ±first order grating diffracted light diffracted by the grating11 or those for the grating diffracted light with the order larger thanthe first order are arranged so as to avoid the stray light of itszero-th order grating diffracted light, a similar effect can beobtained. Further, if the stray light of the regions in the Raddirection with respect to the grating center is separated from eachother in the Rad direction, while the stray light of the regions in theTan direction with respect to the grating center is separated from eachother in the Tan direction, a similar effect can be obtained. Forexample, even if the light receiving parts e1, f1, g1, and h1 arearrayed in the Rad direction as illustrated in FIG. 12 for the opticalbeams diffracted by the regions Dh, De, Df, and Dg (region A) theregions of which on the grating are separated from each other in the Tandirection, a similar effect can be obtained. In addition, the lightreceiving parts a1, b1, c1, d1, e1, f1, g1, and h1, and the lightreceiving part for detecting the focus signal may be arrayed so as toform an approximately circular shape with respect to the zero-th ordergrating diffracted light as illustrated in a dotted line 24 of FIG. 12.

The optical pickup device according to the present embodiment ischaracterized by a construction in which the stray light is preventedfrom entering the light receiving part, and does not depend upon themethods for detection and the calculations of the focusing error signaland the tracking error signal. Further, there is no the need for both ofthe light receiving parts to be contacted with each other. Although, inthe present embodiment, the +first order grating diffracted light andthe −first order grating diffracted light of the region Di were notspecified, for example, the +first order grating diffracted light andthe −first order grating diffracted light may be diffracted in the Raddirection, and signals for adjustment and other servo signals such as aspherical aberration error signal may be detected by using them.Although in the present embodiment, the −first order grating diffractedlight diffracted by the regions De, Df, Dg, and Dh was not detected, byproviding additional light receiving part, the −first order gratingdiffracted light may be detected as the RF signal, the focusing errorsignal, the tracking error signal, and the signals for adjustment. Inlight of the above-description, the −first order grating diffractedlight diffracted by the regions De, Df, Dg, and Dh may be detected asillustrated in FIGS. 13A and 13B to generate the focusing error signal.Further, based on a similar idea, the −first order grating diffractedlight diffracted by the regions Da, Db, Dc, and Dd and the +first ordergrating diffracted light diffracted by the regions De, Df, Dg, and Dhmay be detected as illustrated in FIGS. 14A and 14B to generate thetracking error signal. Furthermore, the +first order grating diffractedlight diffracted by the remaining regions Da, Db, Dc, and Dd and the−first order grating diffracted light diffracted by the regions De, Df,Dg, and Dh may be detected to generate the focusing error signal.Furthermore, based on a similar idea, the −first order gratingdiffracted light diffracted by the regions Da, Db, De, and Dh and the+first order grating diffracted light diffracted by the regions Dc, Dd,Df, and Dg may be detected to generate the tracking error signal asillustrated in FIG. 15A, while the +first order grating diffracted lightdiffracted by the regions Da, Db, De, and Dh and the −first ordergrating diffracted light diffracted by the regions Dc, Dd, Df, and Dgmay be detected to generate the focusing error signal. Alternatively, asillustrated in FIG. 15B, the −first order grating diffracted lightdiffracted by the regions Db, Dd, De, and Dh and the +first ordergrating diffracted light diffracted by the regions Da, Dc, Df, and Dgmay be detected to generate the tracking error signal, while the +firstorder grating diffracted light diffracted by the regions Db, Dd, De, andDh and the −first order grating diffracted light diffracted by theregions Da, Dc, Df, and Dg may be detected to generate the focusingerror signal. In addition, the output signals from the optical pickupdevice may be reduced by connecting the light receiving parts withwires.

Third Embodiment

FIG. 16 illustrates light receiving parts of a photodetector of anoptical pickup device according to a third embodiment of the presentinvention. A structural difference from the first embodiment is thephotodetector 10 and the other structural elements of the secondembodiment are similar to those of the first embodiment.

The grating 11 illustrated in FIG. 2 is formed by the regions De, Df,Dg, and Dh (region A) entered by only the zero-th order disc diffractedlight of the disc diffracted light diffracted by the tracks on theoptical disc, the regions Da, Db, Dc, and Dd (region B) entered by thezero-th order disc diffracted light and the ±first order disc diffractedlight of the disc diffracted light, and the region Di (region C).

Suppose that a spectral ratio of the grating 11 is, for example, thezero-th order grating diffracted light: the +first order gratingdiffracted light: the −first order grating diffracted light=10:1:1. Thephotodetector 10 has a pattern as illustrated in FIG. 16. In thedrawing, black points illustrate the zero-th order grating diffractedlight and the ±first order grating diffracted light diffracted by thegrating 11. In this case, the zero-th order grating diffracted lightdiffracted by the regions Da, Db, Dc, Dd, De, Df, Dg, Dh, and Di of thegrating 11 enters the light receiving part j of the photodetectorillustrated in FIG. 16. Further, the +first order grating diffractedlight diffracted by the regions Da, Db, Dc, Dd, De, Df, Dg, and Dh ofthe grating 11 enters the light receiving parts a1, b1, c1, d1, e1, f1,g1, and h1, respectively. Further, the −first order grating diffractedlight diffracted by the regions Da, Db, Dc, and Dd enters the lightreceiving parts r3, s3, t3, u3, and v3 for detecting a focusing errorsignal. The −first order grating diffracted light diffracted by theregions De, Df, Dg, and Dh enters the light receiving parts e2, f2, g2,and h2, respectively. Signals J0, A1, B1, C1, D1, E1, F1, G1, H1, E2,F2, G2, H2, R3, S3, T3, U3, and V3 obtained from the light receivingparts j, a1, b1, c1, d1, e1, f1, g1, h1, e2, f2, g2, h2, r3, s3, t3, u3,and v3 are calculated as follows to generate the focusing error signal(FES), the tracking error signal (TES), and the RF signal (RF).

$\begin{matrix}{\mspace{79mu} {{{FES} = {\left( {{R\; 3} + {T\; 3} + {V\; 3}} \right) - \left( {{S\; 3} + {U\; 3}} \right)}}{{TES} = {{\left\{ {\left( {{A\; 1} + {B\; 1}} \right) - \left( {{C\; 1} + {D\; 1}} \right)} \right\} - {{kt} \times \left\{ {\left( {{E\; 1} + {E\; 2} + {F\; 1} + {F\; 2}} \right) - \left( {{G\; 1} + {G\; 2} + {H\; 1} + {H\; 2}} \right)} \right\} \mspace{79mu} {RF}}} = {J\; 0}}}}\mspace{40mu}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Note that a symbol kt is a coefficient so as not to generate a DCcomponent by the tracking error signal when the objective lens isdisplaced. In this case, for example, the knife edge method is used asthe focus error detection method.

FIG. 17 illustrates a relationship between the signal light and thestray light from the other layers during the recording and reproducingoperations of the dual layer disc. FIG. 17 (a) illustrates arelationship between the signal light and the stray light from the otherlayers during the recording and reproducing operations of the L0 layer,and (b) illustrates a relationship between the signal light and thestray light from the other layers during the recording and reproducingoperations of the L1 layer. Here, one stray light O0 and another straylight O1 illustrate the zero-th order grating diffracted light of straylight from the other layers at the L0 layer and the L1 layer,respectively. As can be seen from FIG. 17, the signal light and thestray light from the other layers do not overlap each other on the lightreceiving part except for the zero-th order grating diffracted lightdiffracted by the grating 11. Note that the signal J0 detected from thelight receiving part j is not used for detecting the tracking errorsignal, but used for the reproduction signal, and therefore, even if thestray light is present, there is no problem from a practical standpoint.

Also as described in the first embodiment, in such a case that regionsof the grating 11 have been separated along the Tan direction withrespect to the optical beam center 15 (namely, regions Dh, De, Df, andDg (region A)), it is desirable that the stray light is avoided alongthe Tan direction. Therefore, by avoiding the stray light along the Tandirection as in the light receiving parts e1 and h1, and f1 and g1 (e2and h2, and 12 and g2) of FIG. 16, the stray light is prevented fromentering the light receiving parts even if the objective lens isdisplaced in the Rad direction.

In such a case that regions of the grating 11 have been separated alongthe Rad direction with respect to the optical beam center 15 (namely,regions Da, Db, Dc, Dd (region B)), it is desirable that the stray lightis avoided along the Rad direction. Therefore, by avoiding the straylight along the Rad direction as in the light receiving parts a1 and b1,and c1 and d1 of FIG. 16, adverse influences caused by the stray lightdiffracted by the other regions can be suppressed to a minimum effect.Further, the optical pickup device can have a construction if thedistances between the light receiving part j and all the light receivingparts except the light receiving part j are widened, the stray lightfrom the other layers of the zero-th order grating diffracted light isprevented from entering the light receiving part even when the straylight moves along with the displacement of the objective lens. Further,when the detection of RF signals is performed by one light receivingpart, noises generated at the time of converting light into electricsignals can be reduced. Therefore, the above-described construction isextremely advantageous from the viewpoint of the improvement in thesignal-to-noise ratio of reproduction signals in the multilayer disc.

According to the present embodiment, the grating 11 is described withreference to FIG. 2, however, it is not limited thereto. For example,even if the patterns as illustrated in FIGS. 7A and 7B are used, asimilar effect can be obtained. Further, for the purpose of eliminatingthe stray light except within an effective diameter of the signal lighton the grating 11, if a region Z is formed on the grating 11 asillustrated in FIG. 8, a similar effect can be obtained. In this case,the grating 11 has a construction such that light entering the region Zis prevented from entering the light receiving parts. The region Z maybe made by a grating structure, a multilayer-film mirror, or a filter.Moreover, in the present embodiment, the grating 11 was arranged at theposition after the optical beam has passed through the beam splitter 52.Alternatively, along with replacing the grating 11 by a polarizingdiffracted grating, if the polarizing diffraction grating may be arrayedat a position before the optical beam passes through the beam splitter52, a similar effect can be obtained. Also, although the optical dischaving two layers has been described in the present embodiment, evenwhen such optical discs having three or more layers are used, a similareffect can be obtained. In addition, as apparent from the foregoingdescription, there is no limitation as to the spherical aberrationcompensation method. The arrangement of the light receiving partsaccording to the present embodiment is one example. If the zero-th ordergrating diffracted light of the grating 11 with a large light amount isdetected using one light receiving part and the light receiving partsfor the ±first order grating diffracted light diffracted by the grating11 or those for the grating diffracted light with the order larger thanthe first order are arranged so as to avoid the stray light of thezero-th order grating diffracted light, a similar effect can beobtained. Further, if the stray light of the regions in the Raddirection with respect to the grating center is separated from eachother in the Rad direction, and when the stray light of the regions inthe Tan direction with respect to the grating center is separated fromeach other in the Tan direction, it goes without saying that a similareffect can be obtained. For example, if the light receiving parts arearranged as illustrated in FIGS. 18A and 18B, a similar effect can beobtained. Further, there is no problem even if the light receiving partsf1, g1, e2 and h2, and those f2, g2, e1 and h1 in FIG. 16, and the lightreceiving parts e1, g1, f2 and h2, and those e2, g2, f1 and h1 in FIG.18A are closely arranged. For example, the light receiving parts may belined in a horizontal direction to detect as illustrated in FIG. 19.

The optical pickup device according to the present embodiment ischaracterized by a construction in which the stray light is preventedfrom entering the light receiving part, and does not depend upon themethods for detection and the calculations of the focusing error signaland the tracking error signal. Further, there is no the need for both ofthe light receiving parts to be contacted with each other. Although, inthe present embodiment, the +first order grating diffracted light andthe −first order grating diffracted light of the region Di were notspecified, for example, the +first order grating diffracted light andthe −first order grating diffracted light may be diffracted in the Tandirection, and signals for adjustment and other servo signals such as aspherical aberration error signal may be detected by using them.Furthermore, it goes without saying that the output signals from theoptical pickup device may be reduced by connecting the light receivingparts with wires.

Fourth Embodiment

FIG. 20 illustrates light receiving parts of a photodetector of anoptical pickup device according to a fourth embodiment of the presentinvention. A structural difference from the first embodiment is thephotodetector 10 and the other structural elements of the presentembodiment are similar to those of the first embodiment.

The grating 11 illustrated in FIG. 2 is formed by the regions De, Df,Dg, and Dh (region A) to which only the zero-th order disc diffractedlight of the disc diffracted light diffracted by tracks on the opticaldisc enters, the regions Da, Db, Dc, and Dd (region B) to which thezero-th order disc diffracted light and the ±first order disc diffractedlight of the disc diffracted light enter, and the region Di (region C).

Suppose that a spectral ratio of the grating 11 is, for example, thezero-th order grating diffracted light: the +first order gratingdiffracted light: the −first order grating diffracted light=10:1:1. Thephotodetector 10 has a pattern as illustrated in FIG. 20. In thedrawing, black points illustrate the zero-th order grating diffractedlight and ±first order grating diffracted light diffracted by thegrating 11. In this case, the zero-th order grating diffracted lightdiffracted by the regions Da, Db, Dc, Dd, De, Df, Dg, Dh, and Di of thegrating 11 enters the light receiving part j of the photodetectorillustrated in FIG. 20. Further, the +first order grating diffractedlight diffracted by the regions Da, Db, Dc, Dd, De, Df, Dg, and Dh ofthe grating 11 enters the light receiving parts a1, b1, c1, d1, e1, f1,g1 and h1, respectively. Further, the −first order grating diffractedlight diffracted by the regions Da, Db, Dc, and Dd enters the lightreceiving parts r3, s3, t3, u3, and v3 for detecting the focusing errorsignal. In this case, the −first order grating diffracted lightdiffracted by the regions De, Df, Dg, and Dh does not enter the lightreceiving parts.

Signals J0, A1, B1, C1, D1, E1, F1, G1, H1, R3, S3, T3, U3, and V3obtained from the light receiving parts j, a1, b1, c1, d1, e1, f1, g1,h1, r3, s3, t3, u3, and v3 are calculated as follows to generate thefocusing error signal (FES), the tracking error signal (TES), and the RFsignal (RF).

FES=(R3+T3+V3)−(S3+U3)

TES={(A1+B1)−(C1+D1)}−kt×{(E1+F1)−(G1+H1)}

RF=J0  [Equation 5]

Note that a symbol kt is a coefficient so as not to generate a DCcomponent by the tracking error signal when the objective lens isdisplaced. In this case, for example, the knife edge method is used asthe focus error detection method.

Since optical spots are arranged on the photodetector in the same manneras in the third embodiment, the stray light from the other layers duringthe recording and reproducing operations of the dual layer disc isprevented from entering the light receiving parts except for the zero-thorder grating diffracted light diffracted by the grating 11. Note thatthe signal J0 detected from the light receiving part j is not used fordetecting the tracking error signal, but used for a reproduction signal.Therefore, even if the stray light is present, there is no problem froma practical standpoint.

Also as described in the first embodiment, in such a case that regionsof the grating 11 have been separated along the Tan direction withrespect to the optical beam center 15 (namely, the regions Dh, De, Df,and Dg (region A)), it is desirable that the stray light is avoidedalong the Tan direction. Therefore, by avoiding the stray light alongthe Tan direction as in the light receiving parts f1 and g1, and e1 andh1 of FIG. 20, even if the objective lens is displaced in the Raddirection, the stray light is prevented from entering the lightreceiving parts. In such a case that regions of the grating 11 areseparated along the Rad direction with respect to the optical beamcenter 15 (namely, the regions Da, Db, Dc, and Dd (region B)), it isdesirable that the stray light is avoided along the Rad direction.Therefore, by avoiding the stray light along the Rad direction as in thelight receiving parts a1, b1, c1, and d1 of FIG. 20, so that adverseinfluences caused by the stray light diffracted from the other regionscan be suppressed to a minimum effect.

As described above, when the light receiving parts are arranged asillustrated in FIG. 20, the photodetector 10 can effectively separatethe signal light from the stray light. Therefore, the photodetector 10can detect the stable tracking error signal. Further, the optical pickupdevice has a construction in which when the distances between the lightreceiving part j and all the light receiving parts except the lightreceiving part j are widened, the stray light from the other layers ofthe zero-th order grating diffracted light is prevented from enteringthe light receiving part even when the stray light moves along with thedisplacement of the objective lens. Further, when the detection of RFsignals is performed by one light receiving part as described above,noises generated at the time of converting light into electric signalscan be reduced. Therefore, the above-described construction is extremelyadvantageous from the viewpoint of the improvement in thesignal-to-noise ratio of reproduction signals in the multilayer disc.

According to the present embodiment, the grating 11 is described withreference to FIG. 2, however, it is not limited thereto. For example,even if the patterns as illustrated in FIGS. 7A and 7B are used, asimilar effect can be obtained. Further, for the purpose of eliminatingthe stray light except within an effective diameter of the signal lighton the grating 11, if a region Z is formed on the grating 11 asillustrated in FIG. 8, a similar effect can be obtained. At this time,the grating 11 has a construction such that light entering the region Zis prevented from entering the light receiving parts. The region Z maybe made by a grating structure, a multilayer-film mirror, or a filter.Moreover, in the present embodiment, the grating 11 was arranged at theposition after the optical beam has passed through the beam splitter 52.Alternatively, along with replacing the grating 11 by a polarizingdiffraction grating, if the polarizing diffraction grating may bearrayed at a position before the optical beam passes through the beamsplitter 52, a similar effect can be obtained. Also, although theoptical disc having two layers has been described in the presentembodiment, even when such optical discs having three or more layers areused, a similar effect can be obtained. Furthermore, if the constitutionis such that the stray light of the regions in the Rad direction withrespect to the grating center is separated from each other in the Raddirection and the stray light of the regions in the Tan direction withrespect to the grating center is separated from each other in the Tandirection, a similar effect can be obtained. For example, if the lightreceiving parts are arranged as illustrated in FIGS. 21A and 21B, asimilar effect can be obtained.

The optical pickup device according to the present embodiment ischaracterized by a construction in which the stray light is preventedfrom entering the light receiving part, and does not depend upon methodsfor detection and calculations of the focusing error signal and thetracking error signal. Further, there is no the need for both of thelight receiving parts to be contacted with each other. Although, in thepresent embodiment, the +first order grating diffracted light and the−first order grating diffracted light of the region Di were notspecified, for example, the +first order grating diffracted light andthe −first order grating diffracted light may be diffracted in the Tandirection, and signals for adjustment and other servo signals such as aspherical aberration error signal may be detected by using them. Whenconsidering the above-described content, the −first order gratingdiffracted light diffracted by the regions De, Df, Dg, and Dh may bedetected as illustrated in FIGS. 22A to 22C to generate the focusingerror signal. Further, based on a similar idea, the +first order gratingdiffracted light diffracted by the regions Da, Db, Dc, and Dd and the−first order grating diffracted light diffracted by the regions De, Df,Dg, and Dh may be detected as illustrated in FIGS. 23A to 23D togenerate the tracking error signal, while the −first order gratingdiffracted light diffracted by the remaining regions Da, Db, Dc, and Ddand the +first order grating diffracted light diffracted by the regionsDe, Df, Dg, and Dh may be detected to generate the focusing errorsignal. Furthermore, based on a similar idea, the +first order gratingdiffracted light diffracted by the regions Da, Db, De, and Dh and the−first order grating diffracted light diffracted by the regions Dc, Dd,Df, and Dg may be detected to generate the tracking error signal asillustrated in FIGS. 24A to 24D, while the −first order gratingdiffracted light diffracted by the regions Da, Db, De, and Dh and the+first order grating diffracted light diffracted by the regions Dc, Dd,Df, and Dg may be detected to generate the focusing error signal. Inaddition, the output signals from the optical pickup device may bereduced by connecting the light receiving parts with wires.

Fifth Embodiment

In a fifth embodiment, optical reproducing apparatus having mounted withan optical pickup device 170 will be described. FIG. 25 illustrates aschematic construction of the optical reproducing apparatus. The opticalpickup device 170 has a mechanism capable of being driven along the Raddirection of an optical disc 100, and is position-controlled accordingto access control signals from an access control circuit 172.

A predetermined laser drive current is supplied to the laser diodewithin the optical pickup device 170 from a laser lighting circuit 177,and laser light is emitted from the laser diode with a predeterminedlight amount according as the reproduction. In addition, the laserlighting circuit 177 can be incorporated into the optical pickup device170.

Signals output from the photodetector 10 within the optical pickupdevice 170 are sent to a servo signal generating circuit 174 and aninformation signal reproducing circuit 175. The servo signal generatingcircuit 174 generates servo signals such as a focusing error signal, atracking error signal, and a tilt control signal based on the signalsfrom the photodetector 10. Based on the servo signals, the servo signalgenerating circuit 174 drives an actuator within the optical pickupdevice 170 via an actuator driving circuit 173, and controls theposition of an objective lens.

The information signal reproducing circuit 175 generates informationsignals recorded on the optical disc 100 based on the signals from thephotodetector 10.

A part of the signals obtained by the servo signal generating circuit174 and the information signal reproducing circuit 175 are sent to acontrol circuit 176. A spindle motor driving circuit 171, the accesscontrol circuit 172, the servo signal producing circuit 174, the laserlighting circuit 177, and a spherical aberration compensation elementdriving circuit 179 are connected to this control circuit 176. Thecontrol circuit 176 performs the rotation control of the spindle motor180 which rotates the optical disc 100, the control of access directionand access position, the servo control of the objective lens, thecontrol of the light amount of the laser diode emission within theoptical pickup device 170, and the spherical aberration compensation dueto a difference of the disc plate thickness.

Sixth Embodiment

In a sixth embodiment, optical recording and reproducing apparatusmounted with the optical pickup device 170 will be described. FIG. 26illustrates a schematic arrangement of the optical recording andreproducing apparatus. The optical recording and reproducing apparatusof this sixth embodiment has the below-mentioned different points fromthat of the optical recording and reproducing apparatus illustrated inFIG. 25: an information signal recording circuit 178 is provided betweenthe control circuit 176 and the laser lighting circuit 177, thereby afunction is added in which the lighting of the laser lighting circuit177 is controlled based upon a recording control signal supplied fromthe information signal recording circuit 178 so as to write desirableinformation to the optical disc 100.

In addition, the present invention is not limited to the above-describedembodiments, but includes various modifications. For example, theabove-described embodiments are described in detail in order to clearlydescribe the present invention, and are not necessarily limited to theoptical pickup device and optical disc apparatus having all thedescribed constructions. Further, a part of constructions according toone embodiment can be replaced by those according to the otherembodiments, and the constructions according to the other embodimentscan be added to that according to one embodiment. Furthermore, it ispossible to delete, or replace a part of the constructions according toeach embodiment with the constructions according to the otherembodiments.

1. An optical pickup device comprising: a laser diode which emits laserlight; an objective lens which irradiates an optical beam emitted fromthe laser diode on an optical disc; and one photodetector which detectsan optical beam reflected by an information recording layer on theoptical disc, wherein the photodetector has one light receiving partwhich detects a reproduction signal.
 2. An optical pickup devicecomprising: a laser diode which emits laser light; an objective lenswhich irradiates an optical beam emitted from the laser diode on anoptical disc; a grating which branches an optical beam; and onephotodetector having a plurality of light receiving parts which detectsan optical beam reflected by an information recording layer on theoptical disc, wherein the photodetector has one light receiving partwhich detects a reproduction signal, and generates a signal forcontrolling a servo signal from all the light receiving parts except thelight receiving part for detecting a reproduction signal.
 3. An opticalpickup device comprising: a laser diode which emits laser light; anobjective lens which irradiates an optical beam emitted from the laserdiode on an optical disc; an actuator which displaces the objective lensin a radius direction of the optical disc; a grating which branches anoptical beam reflected by an information recording layer on the opticaldisc into a plurality of regions; and one photodetector having aplurality of light receiving parts which receives optical beams branchedby the plurality of regions on the grating, wherein: the photodetectorhas a first light receiving part which detects zero-th order gratingdiffracted light of the grating and a plurality of second lightreceiving parts which detects grating diffracted light having an ordermore than or equal to that of ±first order grating diffracted light; adetected signal of the zero-th order grating diffracted light of thegrating is defined as a reproduction signal; and a detected signal ofthe grating diffracted light having an order more than or equal to thatof the ±first order grating diffracted light is defined as a signal forservo controlling.
 4. The optical pickup device according to claim 3,wherein when focusing on an intended information recording layer of theoptical disc, the plurality of second light receiving parts on thephotodetector are arranged outside the zero-th order grating diffractedlight of an optical beam reflected by all the recording and reproducinglayers except the intended information recording layer of the opticaldisc.
 5. The optical pickup device according to claim 3, wherein whenfocusing on an intended information recording layer of the optical disc,the first light receiving part on the photodetector is arranged outsidethe grating diffracted light having an order more than or equal to thatof the ±first order grating diffracted light of an optical beamreflected by all the recording and reproducing layers except theintended information recording layer of the optical disc.
 6. The opticalpickup device according to claim 3, wherein the second light receivingparts of the photodetector are arranged in a shape of a substantialcircular arc or a substantial circle such that the first light receivingpart of the photodetector is substantially centered.
 7. The opticalpickup device according to claim 3, wherein when focusing on theintended information recording layer of the optical disc, an opticalbeam reflected by the intended information recording layer focuses on alight receiving part of the photodetector.
 8. The optical pickup deviceaccording to claim 3, wherein a light amount of the zero-th ordergrating diffracted light is larger than that of the grating diffractedlight having an order more than or equal to that of the ±first ordergrating diffracted light of the grating.
 9. The optical pickup deviceaccording to claim 3, wherein: the grating has at least three sets ofregions A, B, and C; among disc diffracted light diffracted by tracks onthe optical disc, the zero-th order disc diffracted light enters theregion A of the grating; at least the ±first order disc diffracted lightenters the region B; the photodetector detects a reproduction signalfrom the zero-th order grating diffracted light diffracted by thegrating regions A, B, and C; and among the light receiving parts whichdetect either the +first order grating diffracted light or −first ordergrating diffracted light of the region A, at least two light receivingparts are arrayed in a substantially straight line along a directionwhich is substantially coincident with a tangential direction of theoptical disc;
 10. The optical pickup device according to claim 3,wherein: the grating has at least three sets of regions A, B, and C;among disc diffracted light diffracted by tracks on the optical disc,the zero-th order disc diffracted light enters the region A of thegrating; at least the ±first order disc diffracted light enters theregion B; the photodetector detects a reproduction signal from thezero-th order grating diffracted light diffracted by the grating regionsA, B, and C; and among the light receiving parts which are the secondlight receiving parts and detect the +first order grating diffractedlight or the −first order grating diffracted light of the region B, atleast two light receiving parts are arrayed in a substantially straightline along a direction which is made substantially coincident with aradial direction of the optical disc.
 11. The optical pickup deviceaccording to claim 9, wherein a tracking error signal is generated froma detected signal of the grating diffracted light diffracted by thegrating region A and a detected signal of the grating diffracted lightdiffracted by the grating region B.
 12. The optical pickup deviceaccording to claim 1, wherein a focusing error signal is detected by adouble knife edge method.
 13. The optical pickup device according toclaim 2, wherein in case of focusing on the intended informationrecording layer of the optical disc, transmissivity in a region of aside outer than a contour of an optical beam that enters the grating ofthe intended information recording layer becomes smaller than that of aninner side.
 14. The optical pickup device according to claim 2, whereinin case of focusing on the intended information recording layer of theoptical disc, in a region of a side outer than a contour of an opticalbeam which enters the grating, optical beams reflected by all therecording and reproducing layers except the intended informationrecording layer are irradiated to a region different from the lightreceiving part of the photodetector.
 15. The optical pickup deviceaccording to claim 2, wherein in case of focusing the intendedinformation recording layer of the optical disc, when optical beamsreflected by all the recording and reproducing layers except theintended information recording layer enters, a region of a side outerthan a contour of an optical beam that enters the grating reflects theentering light.
 16. Optical disc apparatus mounted with the opticalpickup device according to claim 1, a laser lighting circuit whichdrives the laser diode used in the optical pickup device, a servo signalgenerating circuit for generating the focusing error signal and atracking error signal by using signals detected by the photodetectorused in the optical pickup device, and an information signal reproducingcircuit for reproducing an information signal recorded on the opticaldisc.